1. Field of the Invention
This invention relates to a system for the synchronization of transmission signal pulses between a key service unit and key telephone sets in a key telephone system which is adapted to transmit, in a time-division pulse signal format, key information or the like between the key service unit and the key telephone sets.
2. Description of the Prior Art
Recently in order to reduce the number of cable conductors of a key telephone system, there have been proposed a variety of systems of transmitting a control signal in the form of a time-division pulse signal. However, they mostly fall into the type that call for synchronization between control circuits of the key service unit and the key telephone sets and provides therefor a synchronizing signal channel separately of a data channel heretofore employed. There has also been proposed a system of transmitting a synchronizing signal over the same channel as data, for example, by using code words different from data signals. In these conventional systems, however, another cable pair is required, and in a case of multiplex transmission using the same cable, a modem or a code detector is needed, resulting in the key telephone system becoming complex.